Properties Of Biochar Derived From Castor Plants

In Latin America, Amazonian natives have been using biochar along with organic waste for centuries or even millennia to enhance the soil and alter its characteristics, creating thus highly-fertile patches in a marginal land. This ancient anthropogenic intervention in agriculture resulted in the long-term establishment of a healthy soil characterized by an increased content of stable organic matter and nutrients, a land known as “Amazonian Dark Earths” or “Terra Preta.”

Biochar is a carbon-rich material with a porous structure, and it differs from charcoal and similar materials by the fact that it has a high fixed carbon content, minimal tars, and a high surface area. When used as a soil amendment, improves soil productivity, carbon storage, or filtration of percolating soil water. The important properties of biochar in relation to its use as a soil amendment are the surface area, porosity, electrical conductivity, pH, water holding capacity, and cation exchange capacity.

Biomass from plants or other organic material can be converted to biochar at high temperature in the absence of oxygen. Biochar has a high carbon content, low H/C ratio and retains most of the nutrients contained in the original biomass (feedstock). The surface area and porosity of biochar generally increase with longer pyrolysis time and higher temperature. The increased surface area is positively correlated to the water holding capacity and porosity. Based on the production conditions and feedstock characteristics, biochar properties both chemical and physical may vary profoundly. Ultimately, each biochar type must be studied in relation to its effect on plants when used as soil amendment.

Researchers from Institute of Applied Biosciences and Chemical Process and Energy Resources Institute of CERTH in Greece produced biochar by slow pyrolysis at 550 °C from castor stalks and de-oiled castor cake, both by-products of castor oil production, in view of sustainable valorization of a potential large-scale cultivation of castor beans. Their work is published in the research journal, Biomass and Bioenergy. The extraction of castor oil generates large amounts of de-oiled castor cake containing ricin, a highly toxic glycoprotein that requires heat treatment prior to its valorization.

The produced biochars were highly alkaline and had significant differences in terms of surface area, morphology, nutrient content, and ratios of atomic C:N and H:C. Castor-derived biochar affected germination and development of castor seedlings but not of tomato seedlings. Specifically, castor stalk-derived biochar affected positively root length and complexity of castor seedlings promoting a well-developed root system.

A less profound but noticeable effect was observed in tomato seedlings. In both species, biochar treatments promoted lateral root initiation but increased the developmental rate only in castor. Furthermore, biochars affected soil cation exchange capacity Based on the results, castor biochars improved castor seed germination, achieving 90% success rate earlier when compared to control. On the contrary, biochar did not affect significantly the germination of tomato seedlings. However, in both species, the biochar treatments promoted lateral root initiation but increased the developmental rate only in castor. In addition, biochars affected soil capacity to retain several macro- and micro-nutrients beneficial for plant growth.

Modern agricultural practices rely on the excessive use of inorganic fertilizers to maintain high yields. Currently, more than half of nitrogen fertilizers applied globally, escape into the environment without being used by crops. Modern agriculture has to overcome issues such as: drought, nutrient leaching, salinity and heavy metal toxicity. Biochar may offer an eco-friendly alternative solution to overcome such issues.